Smith, P., Heath, D., and Hasleton, P. S. (1973).Thorax, 28, 559-566. Electron microscopy of chlorphentermine lung. Electron microscopy of lung tissue from rats treated with chlorphentermine shows an intense hyperplasia in the alveolar walls of granular pneumocytes which remain attached and do not migrate into the alveolar spaces. Numerous `foam cells' are found free in the alveoli and are histiocytes which have ingested osmiophilic lamellar bodies. Similar laminated inclusions are found in granular pneumocytes, membranous pneumocytes, bronchiolar Clara cells, pulmonary macrophages, and endothelial cells of pulmonary capillaries. The intra-alveolar debris is rich in osmiophilic lamellar bodies with associated phospholipid lattices. The appearances are those of a toxic alveolitis. Further studies of chronic toxicity are suggested to ascertain if this acute lesion progresses to fibrosing alveolitis.